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motor:
Have a gen 3 , 5.3 motor.
706 heads with btr springs, hardened pushrods,
ls7 lifters, btr stage 2 turbo cam,
arp head studs, ls7 head gaskets, arp rod bolts(resized rods), no name pistons .5mm larger than stock.
I would really like to see what’s needed for me to rev higher with my current setup. I own a dyno, I’m going to put it on tmr and see how bad power falls off if I rev higher. even if tq continues falling, if HP carries without dropping then I would benefit using that extra rpm? Or should I just be shifting around my current 6200ish because tq hasent dramatically dropped out?
Based on current graph, appears hp will peak around 6300. Yes, you'll benefit with more rpm until the hp starts dropping off. Street car? Post new graph once you've run it out past 6800. The heads flow a lot more than you're currently using. Maybe someone will chime in that knows the mcsa of the 706/862 to get an idea of what theoretical rpm limit is at 328ci. I'm guessing around 7300. Depending on use, you may not want a motor that runs 3500 to 7500.
Side note - See where your rpm drops back on the shift compared to peak tq to figure where best shift rpm is. Trap rpm typically ~400 higher than pk hp for best results.
Based on that Dyno graph it hasn't even nosed over yet. That cam on a 5.3 should be revved much higher. You're basically shifting at the stock redline. Shift at 7 or 7200 and see what it picks up in ET.
What an exciting day... played with car today for few hours on the dyno. Tuned boost up to 22psi, adjusted timing top end so it dropped from 14* around 16-17psi to about 11* from 20-22psi.
I should for sure hit my mid 5s 60-130 now. Picked up around 130whp/tq.
as for original post, I revved to 6800 entire time. Car carried HP whole time. Obviously tq dropped off. No idea why I’ve been shifting at 6k whole time. Dyno sheet says 6200 but really I was 6800. My dyno uses rpm by speed because my sensor box is broke ATM. Even calibrated before runs, it reads slightly off. Should I try revving higher than the 6800?
hoping I can be mid 5s now. Car is street car. Went to track couple weeks ago and I trapped 131 now that I’m T56 with no launch. Just rolled out because I drove car hours to track and had to make it home. Already snapped my axel on first launch lol. Automatic in car last year I trapped 135 with a 6.8 60-130 🤷🏻♂️. Don’t really care about track data in this car. Just for fun.
Curious if you have an intercooler or not, or just the 93 and spray. I don't have room for an IC'er ,but run 93, but keep the boost low, MAT's still hit 180's on a quick street hit.
Curious if you have an intercooler or not, or just the 93 and spray. I don't have room for an IC'er ,but run 93, but keep the boost low, MAT's still hit 180's on a quick street hit.
Yes, rev it higher. Do a 3rd gear pull and bring it to 7500. See where it starts to fall off. That intake will limit you soon IMO. You could get a short runner intake that will clear the hood and it will really shine from 6k and up. But you'd lose a ton down low. May not be desirable with a t56, but ideally you want to make the big power past 6k on most SBE's. Also not sure if your syncros will like going into gear at big rpm. But I'd let it pull until it stops pulling. Then shift 200-500rpm above that.
Last edited by Forcefed86; Jun 1, 2021 at 01:14 PM.
Yes, rev it higher. Do a 3rd gear pull and bring it to 7500. See where it starts to fall off. That intake will limit you soon IMO. You could get a short runner intake that will clear the hood and it will really shine from 6k and up. But you'd lose a ton down low. May not be desirable with a t56, but ideally you want to make the big power past 6k on most SBE's. Also not sure if your syncros will like going into gear at big rpm. But I'd let it pull until it stops pulling. Then shift 200-500rpm above that.
7500!!! That would be pretty awesome to be in gear that long. I don’t wanna lose my down low. I’m happy now, being able to get to 7000 or more rpm off what I have would be phenomenal honestly.
I have the magnum trans with synchromesh fluid. Hope the trans would be ok.
7500!!! That would be pretty awesome to be in gear that long. I don’t wanna lose my down low. I’m happy now, being able to get to 7000 or more rpm off what I have would be phenomenal honestly.
I have the magnum trans with synchromesh fluid. Hope the trans would be ok.
Don't float the valves, but yea. The common consensus these days is the more you rev and apply power after 6k (past pk tq really) the easier it is on the bottom end. Which is the main concern with an SBE. It may not pull to 7500 with that intake, let up when it nose dives. But 7500 isn't super hard on things these days assuming you have the spring to control it. The SBE record holders are turning around 8300rpm for example. Lots of load at low rpm is what breaks things.
Nothing wrong with your trans or fluid. But the syncros that allow the gears to align are really working overtime at big RPM. I had issues getting a full faced sprung clutch into gear past 7k. Switched to an un-sprung MUCH lighter weight 4 puck and I could shift over 7k no problem. (totally different trans, but same rules apply).
Don't float the valves, but yea. The common consensus these days is the more you rev and apply power after 6k (past pk tq really) the easier it is on the bottom end. Which is the main concern with an SBE. It may not pull to 7500 with that intake, let up when it nose dives. But 7500 isn't super hard on things these days assuming you have the spring to control it. The SBE record holders are turning around 8300rpm for example. Lots of load at low rpm is what breaks things.
Nothing wrong with your trans or fluid. But the syncros that allow the gears to align are really working overtime at big RPM. I had issues getting a full faced sprung clutch into gear past 7k. Switched to an un-sprung MUCH lighter weight 4 puck and I could shift over 7k no problem. (totally different trans, but same rules apply).
so I revved car out to 7k and it started leaning out to 11.8. Had to raise fuel pressure to get everything nice for the 6800. For some reason the boost started dropping from 250kpa to 240kpa 6800-7k rpm too. So I didn’t bother revving out. Just left it at the 6800rpm. It’s too bad though cause it would’ve went more. I didn’t realize I was pushing my 80lb dekas so much at those higher rpm. Duty cycle was like 105 I think he said after 6800.
i had someone remote in after he looked at my tune logs... guy cleaned up my down low driving and my air fuels under boost when meth was on. I think I’m done pushing this motor for good this time. Gen 3 rods and unknown pistons. Nervous what’s going happen when this thing let’s go. Not bad for some cxracing gt35s lol.
note: the rpm was 6800 but dyno reading was slightly off.
And now this thread has made me question my own setup...
I'm revving a 5.3 to about 6800 on a summit stage 3 turbo cam, pac springs, chromo-pushrods, etc... a 75mm compressor 83x75mm turbine 1.10ar T4 single and a tube header log manifold with a factory truck intake, 20psi. The cam specs say it's good for 7000+ and the summit guy on here said the same in a few cam threads here. But it feels like it just stops pushing at 6800-7000RPM.
I have plenty of injector and fuel pressure left...so what's holding it back?
And now this thread has made me question my own setup...
I'm revving a 5.3 to about 6800 on a summit stage 3 turbo cam, pac springs, chromo-pushrods, etc... a 75mm compressor 83x75mm turbine 1.10ar T4 single and a tube header log manifold with a factory truck intake, 20psi. The cam specs say it's good for 7000+ and the summit guy on here said the same in a few cam threads here. But it feels like it just stops pushing at 6800-7000RPM.
I have plenty of injector and fuel pressure left...so what's holding it back?
truthfully, the turbos would’ve kept going. We had to raise the fuel pressure after it had entire tune on it because fuel drop off right up top. I didn’t have any idea the injectors were maxed like that. If meth ever shuts off, even with the timing drop, my motor prob done.
as to the rpm situation, my boost is odd. If the tune has to much fuel or to lean or timing to low, I’ll have creep or boost drop. Only when the tune is clean does my car get a nice boost curve. So because the leaner situation up top due to injectors, the boost wouldn’t stay up. Without fixing fuel I couldn’t fix boost, so no point in bothering at this point. Cars already pretty pushed lol. I don’t think I was limited in rpm due to anything except fueling.
I don’t think I’ll be much help to you for advice on yours. Your intake supposed flow better than my ls1 and you have larger cam. Turbo hot side seems bigger than my buddy who has a 75/76mm single on his 5.3 and he’s never had an issue revving. We only stopped on his car because pump gas only. Still made 650 on like 13psi. He’s got a stage 2 can only also.
Pretty darn good good gt35s! I'd be happy with that. mine did 560/600 at 11psi with the .6x AR t3 gt35's. Had 241 heads tho, no IC, baby "GM hot cam" and a th400. They are pretty great turbos for the $ IMO! Need to add a 3rd!
Should be able to adjust the map cells for that rpm range and not touch pressure. Do you log fuel pressure? Does it fall at higher RPM? Sure you aren't out of pump? Might also monitor voltage as the factory alternators often stop charging much above 6k. If the alt drops offline it can cause dead time issues with the injectors and spark/fueling issues. My voltage would drop to mid 11's over 6k. That would cause the fuel pump output/flo/pressure to drop drastically. also screwed with injector timing.
If IDC is over 100%, but you're dropping pressure, IDC may not actually be over 100% with steady pressure. Likely the pump struggling. Boost referenced FPR?
truthfully, the turbos would’ve kept going. We had to raise the fuel pressure after it had entire tune on it because fuel drop off right up top. I didn’t have any idea the injectors were maxed like that. If meth ever shuts off, even with the timing drop, my motor prob done.
as to the rpm situation, my boost is odd. If the tune has to much fuel or to lean or timing to low, I’ll have creep or boost drop. Only when the tune is clean does my car get a nice boost curve. So because the leaner situation up top due to injectors, the boost wouldn’t stay up. Without fixing fuel I couldn’t fix boost, so no point in bothering at this point. Cars already pretty pushed lol. I don’t think I was limited in rpm due to anything except fueling.
I don’t think I’ll be much help to you for advice on yours. Your intake supposed flow better than my ls1 and you have larger cam. Turbo hot side seems bigger than my buddy who has a 75/76mm single on his 5.3 and he’s never had an issue revving. We only stopped on his car because pump gas only. Still made 650 on like 13psi. He’s got a stage 2 can only also.
I had that issue too...put a boost-a-pump 17.5v on the walbro400 and now it runs 58-85psi of fuel pressure on the referenced regulator and I only see duty cycles on deka 80's of 70% at 85psi fuel pressure and 22psi of boost. Before the boost-a-pump I was 100% tapped out at 15psi of boost and losing fuel pressure starting at about 12psi. It would drop from 58psi to 44psi in boost as boost psi went up.
Pretty darn good good gt35s! I'd be happy with that. mine did 560/600 at 11psi with the .6x AR t3 gt35's. Had 241 heads tho, no IC, baby "GM hot cam" and a th400. They are pretty great turbos for the $ IMO! Need to add a 3rd!
Should be able to adjust the map cells for that rpm range and not touch pressure. Do you log fuel pressure? Does it fall at higher RPM? Sure you aren't out of pump? Might also monitor voltage as the factory alternators often stop charging much above 6k. If the alt drops offline it can cause dead time issues with the injectors and spark/fueling issues. My voltage would drop to mid 11's over 6k. That would cause the fuel pump output/flo/pressure to drop drastically. also screwed with injector timing.
a third lol!!! I’m tad nervous to go drive the thing and do my 60-130 now with so much more tq. Last time it was 6.1 revving 6k rpm only with 718tq and 68x HP.
i logged the voltage. It drops at high rpm below 12v. Damn that’s gotta be it then. My regulator is boost referenced. I don’t log fuel pressure with stock ecu but my dyno has the sensor. I’ll use that next time.
If IDC is over 100%, but you're dropping pressure, IDC may not actually be over 100% with steady pressure. Likely the pump struggling. Boost referenced FPR?
it is boost referenced. I was just saying that my voltage in logs DO drop below 12 at high rpm.
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Higher revving turbo 5.3 
